feipoa wrote on 2025-10-04, 15:19:

Because I could only get up to 3.72 V with Vin=5V, I resorted to connecting the switching reg to the 12 V rail. I ran it 10 minutes at 3.85 V in Win95 without any trouble, however the switching reg was getting warm, or 63 C. I'm not sure how hot it will get after 2 hours. I guess I need to add a heatsink or fan to the VRM module. It might be easier (and with less heat generation) to use an ultra low drop-out linear regulator with Vin=5V and ditch the switching.

Maybe there's other packaged switching regulator modules which have less drop-out than my LM2596S. I'm curious to know if the switching regulator IC on bertrammatrix's buck module can reach at least 4 V when tied into 5V...?

Yes I was able to get a little above 4 volts with a 5 volt input - I didn't really try going much higher so not sure exactly how high it would go with that input, but it's reasonable to assume it wouldn't quite get to input voltage. IIRC the modules I got claimed around 30volts input capable, and actually came with a little stick on heatsink (meant for the plastic side?) however I did not feel the need to use it at 5 volts (barely warm).

I cleaned some wiring as well, just a little "dongle" now out of spare wires/connectors

Now, a word of caution with these modules, and the reason why I am currently running the boards own regulator again - while this gives the opportunity to very easily mess around with the voltage with a wider range then just the 3-4 volt resistor mod there is one big drawback - the modules output voltage is actually not regulated so to say, but rather tied directly to the input voltage, with the potentiometer only acting as a 0-100% input to output setting, not an actual voltage setting. So - when I observed my 5volt rail change by 0.2-0.3 volts between cold and hot - that difference showed right up on the modules output...YIKES, that's a lot of variation if I'm trying dial in by 0.05 volts

To me that only makes this circuit suitable for testing, unless one has a PSU with a rock solid, zero variation output

I haven't noticed the voltage swings on my switching module when drawn from the 12 V source. Could the upwards of 0.3 V swing at the output on your regulator be related to the drop-out when taken from the 5 V rail? My unit has LM2596S. What does yours have - XL4015 ?

EDIT: These regulators use cheap trimmers and I noticed that just a hair of a turn yields considerable change in voltage. This could also be at play. I plan on swapping my trimmer for a proper Bourns. I replaced the 10K trimmer on my module with a Bourns 1K and this offers much finer voltage adjustment.

I decided that since I've already put so much time into the cabling, that I would add a heatsink and a 30 mm pi fan. Its only about 1.2 CFM, but so far, the VRM's temp has stayed under 32 C, open case.

Added mods: